The invention generally relates to strut type suspension members for vehicles, but more particularly, the invention relates to a strut with an airspring having a sleeve with a flexible wall including a rolling lobe between telescoping members, but more particularly, the invention relates to a strut with an airspring arranged to provide side load compensation while simultaneously providing a sleeve arrangement that gives a rolling lobe an acceptable flexural life and a method for imparting a side load force to a vehicle suspension.
A strut of a vehicle suspension is typically oriented at an angle in relation to a reciprocal movement of a suspension for a wheel. The angular arrangement of the strut introduces a bending moment or torque into the telescoping members of the strut. Should such a moment be not countered or compensated with an opposite moment, it causes telescoping members of the strut to bind and results in vehicle ride harshness and reduced life of the strut. An opposite bending moment introduced into a strut is generally referred to in the industry as "side load compensation".
Airspring configurations have been disclosed with geometries that provide a compensating moment or side load compensation in a telescoping strut to oppose the moment placed on the strut by a vehicle suspension system. Examples of such airspring configurations for telescoping struts are disclosed in U.S. Pat. No. 4,688,774 to Warmuth, and divisional patent thereof, U.S. Pat. No. 4,911,416. The claimed feature of Warmuth '416 pertains to a tubular flexible member (airspring sleeve) with an end cut in a non-perpendicular plane and which end forms a rolling lobe of the airspring. In FIGS. 1 and 2 of Warmuth and herein exemplified by FIG. 2 the so formed rolling lobe Y-Z, Y'-Z' is of unequal length W-Z, W'-Z' when pressed against a rolling lobe surface of a piston of the airspring. The unequal axial length lobe results in a differential area where the force on one side of the piston (i.e. the inboard side of the strut) is greater than the force on the opposite side of the piston (i.e. the outboard side of the strut) causing some degree of side load compensation that counters a moment introduced into the strut by the suspension system. The asymmetry of unequal axial lobe length introduces a problem which is a substantially shortened flexural cycle life of the lobe (e.g. less than 100,000 cycles).
Another problem that an airspring sleeve with a non-perpendicular cut end introduces is that it defines a chamber where the surface area on the outboard side may be less than an inboard side because the sleeve length X'-W' on the outboard side is less than the sleeve length X-W on the inboard side as shown in FIG. 2. The unequal sleeve lengths X'-W', X-W results in a differential surface area in the chamber portion that causes a negative side load force which is counteractive to the side load force desired from the unequal axial length rolling lobe. In FIG. 3 the length of the sleeve forming the rolling lobe portion Y-Z, Y'-Z' is less than the sleeve length that forms the chamber portion X-Y, X'-Y'. However, in FIGS. 5-7 of Warmuth '416 (and herein exemplified by FIG. 3), the chamber portion is substantially formed along length R-S, R'-S' by a metal can. That part of the sleeve length which forms the rolling lobe portion S-T, S'-T' is substantially greater than that part of the sleeve which connects to the can. Consequently, there is very little sleeve length S-U available to form part of the chamber portion.
In Warmuth '774, FIGS. 5-7, an airspring with a piston eccentrically located in relation to a center line for a strut is disclosed in conjunction with a rolling lobe of unequal axial length. While the unequal length rolling lobe provides some side load compensation, the unequal length lobe is detrimental to lobe life as above discussed. In Warmuth FIG. 6, the lobe on the outboard side of the strut is greater in length than that of the lobe on the inboard side which, under Warmuth FIG. 3, imparts negative side load compensation (i.e. in the wrong direction). Also, in FIG. 6, the closure member attaching an end of the sleeve to the can is tilted clockwise while an axis of the sleeve faces toward the inboard side; a free length of the sleeve to where it bends at the rolling lobe has substantially the same projected length on both sides of the piston. Consequently, a difference in the free length of the sleeve per se on the inboard and outboard side is not available to define a differential area that may contribute to a side load compensation.
In FIG. 7 of Warmuth '774 (herein exemplified by FIG. 3), an airspring with rolling lobes of unequal axial lengths is shown. The rolling lobe length T-U against the piston on the inboard side is longer than the length T'-U' of the rolling lobe against the piston on the outboard side which, according to the teaching of Warmuth, provides side load compensation with a clockwise moment. One end of the sleeve is attached to a can that primarily forms a chamber of the airspring and where the closure member attaching and end of the sleeve to the can ring is tilted counterclockwise. The free length S-U of the sleeve to the formation of the rolling lobe on the inboard side is substantially longer than the free length S'-U' of the sleeve of the rolling lobe on the outboard side of the sleeve. The difference in length creates a surface area that is larger on the inboard side which also has a compensating moment which in this case is counterclockwise. Warmuth '774, does not consider any impact that the differential surface area has on side load compensation. The effect of differential surface area may completely offset or negate that side load compensation realized by the effect of a rolling lobe having unequal axial lengths.
Another airspring type strut with side load compensation is disclosed in U.S. Pat. No. 4,712,776 to Geno. As shown in FIG. 2 of Geno, an airspring has lobes of unequal axial lengths. The unequal length lobes have a detrimental impact on flexural life as above discussed in reference to Warmuth. In Geno, side load compensation is generated by means of a rigid member located inboard and attached to a can or canister portion that forms part of the airspring. The member restricts an outward expansion of the flexible sleeve on the inboard side. The sleeve exerts a pressure on the member which results in force on the strut to counteract lateral forces acting on the strut so as to provide a side load compensating moment. The sleeve and piston are arranged coaxially with the center line of the strut, and the canister forms a part of the operating volume for the airspring member.
U.S. Pat. No. 4,763,883 to Crabtree discloses another example of a strut at FIG. 13 where an airsleeve is oriented coaxial with the longitudinal axis of a strut. The airsleeve forms a chamber having a substantially larger diameter than that of the rolling lobe portion of the sleeve. However, Crabtree does not disclose a strut having a means for providing side load compensation.